Field of the Disclosure
The invention relates to a sensor for detecting a periodic magnetic field, comprising a measuring assembly integrating at least one magnetoresistive element the electrical resistance of which varies as a function of the amplitude of the component of said magnetic field in one direction, as well as a system for determining at least one movement parameter of a member able to move with respect to a fixed structure.
Description of the Related Art
In numerous applications, it is wished to know, in real time and with optimum quality, at least one parameter of linear and/or angular movement of a movable member, such as its position, its velocity, its acceleration or its direction of movement.
To do this, the document WO 2006/064169 proposes the use of an encoder intended to be secured to the movable member and which is arranged to deliver a pseudosinusoidal magnetic field at a reading distance from a sensor comprising a plurality of sensitive elements.
To determine a movement parameter of the movable member as a function of the change in the magnetic field, the sensor comprises an electronic circuit arranged so as to use the variations in electrical resistance of the sensitive element in order to deliver a signal representing the magnetic field to be detected.
In particular, the document WO 2006/064169 provides for the sensitive elements to be integrated in an assembly for measuring in a current loop in order to combine signals representing the resistance of each of the sensitive elements so as to deliver two signals in quadrature and of the same amplitude, which can be used for calculating the parameter. The connection of sensitive elements in a Wheatstone bridge is also known.
Advantageously, each sensitive element may comprise at least one pattern based on a magnetoresistive material, in particular with a tunnel effect (TMR, standing for tunnel magnetoresistance), the resistance of which varies as a function of the magnetic field, as for example described in the document WO 2004/083881.
In particular, each pattern then comprises two conductive layers between which an insulating layer is disposed so as to form a succession of tunnel junctions in a measuring assembly. The conductive layers form respectively a magnetic layer sensitive to the field to be measured and a reference magnetic layer, the electrical resistance between the conductive layers being dependent on the relative orientation of the magnetisation of each of said layers.
To do this, the sensitive and reference layers each comprise a magnetic anisotropy direction that are perpendicular while being arranged so as to cause, by relative rotation, a variation in electrical resistance that is linear over a magnetic field range to be detected.
However, adjusting the anisotropy of the sensitive layer may be complex, in particular to attempt to make it insensitive to the different temperature and magnetic field conditions to be detected. Achieving this anisotropy moreover makes it more tricky and expensive to manufacture the sensitive layers. Thus, under certain temperature and/or magnetic field conditions to be detected, this implementation does not give complete satisfaction in that the correct perpendicularity of the magnetic anisotropies is not sufficiently ensured to guarantee good linearity of detection.
The document U.S. Pat. No. 2007/047152 describes the use of a polarisation magnet to measure the magnetic field of a magnet to be detected by means of a magnetoresistive element, in which the magnetic field of the polarisation magnet is arranged so as to suppress the magnetisation of the free layer of said magnetoresistive element and to reduce the rotation angle of the magnetised vector.